As the others said: not needed, but that doesn't take away that it is a nice to have.
However I can't complain about the posting efficiency from my iPhone, it sometimes even goes faster then with the browser on a PC.

Well as a new player, I won't mind the recruitement channel on default. But I wouldn't mind it missing like it is now either. I've picked up the trial to try out the game not to look for a corp at start, I always try to get tot know the basic game mechanics and decide if the game as lasting power for me before I start looking for a corp. This process takes roughly two weeks for me.

However what certainly has to be stated more clearly is where to look for recruitement, by for instance putting the link to the channel as a message somewhere as long as a player hasn't joined a corporation. Or a separate button at the top and include this in the tutorial to be mentioned.

I did the same, but if you ask me that shouldn't be the main reason for the lock. A trial is to test out the game and being locked out of a mechanic that is a major part isn't showing people really what the game is like.

But somehow I agree with the lock as I can imagine that the market is pretty fragile with the current number of players and making it available to trials would possible ruin it.

Now for if there are other and better systems? Probably some can be found, but the suggested in the OP is indeed not going to help much. A limit will only slow down the process a little as you will need only to make more trials to get the amount you want.

What however could work is setting up a sub-market for trials, what do I mean with this. It is the market but only accessible for trial accounts. Of course you won't find big stuff in there as a trial account is pretty limited in what he can make and produce. To solve this let non-trials also be able to make sell orders but not buying anything of it. There should be also a restriction of a maximum of NIC a non-trial account can put on there each month. Like a sell orders that max out to a maximum of 500k NIC each month, and the total NIC of sell orders on that market may not exceed that. So if a non-trial puts up sell orders for 500k NIC and those aren't sold in the month they won't be able to add more the next month, or until some of the older orders are sold.

Another limit to this sub-market would be the type of items that can be sold on there. Like for robots only the small ones. And for weapons only the light and perhaps some medium. And resources perhaps as well for the limit.

This way the trial members will have a market (though limited) to enjoy, and the amount of NIC to get out of the market is limited to 500k NIC/month for a paid account. This limit could be researched more to not screw the full market. But the limit shouldn't be put on a per trial account (as the OP suggestion) only as that will just favour the creation of more trials to exploit the market.